Russianforces have taken control of aUkrainianborder guard post in western Crimea, trapping 30 personnel inside.

The latest move by the Russians to tighten their grip on Crimea was made without the firing of guns – unlike on Saturday, when a Ukrainian border patrol plane was fired at, and European monitors trying to enter Crimea were repelled by "warning shots" from balaclava-clad militias.

The capture of the Chernomorskoye border post – the 11th so far – unfolded without bloodshed before dawn.

Russian forces' seizure of the southern Ukrainian region, which began 11 days ago, has been without open combat. Ukrainian troops are trapped in a number of bases but have offered no armed resistance.

The latest seizure came as William Hague demanded Russia joins formal negotiations over the crisis in Ukraine, as pressure grows for talks under the terms of a treaty in which the Kremlin guaranteed the independence of the former Soviet state.

A convoy of military vehicles, at least 60, bearing no license plates travels on the road from Feodosia to Simferopol (AP)

Four party talks between Russia, US, Britain and Ukraine under the Budapest Memorandum offer a proposed route out of the crisis that has erupted since Russia took control of the Crimean peninsula and threatened further intervention on behalf of Russian-speaking populations in the east.

The Foreign Secretary told BBC One's Andrew Marr programme that Russian had obligations to get involved in direct talks.

"We want see diplomatic progress on Ukraine. We want to see tensions reduce," he said. "It is in our national interest that international treaties and laws are upheld."

Vitaly Klitshko, a former world boxing champion and leading candidate for Ukraine's May presidential elections, also demanded that the countries that guaranteed Ukraine's integrity begin negotiations to end the Russian intervention.

"This is an aggression against our country," he told a meeting in Donetsk, in the Russian speaking east. "We expect in the next couple of days a meeting under the Budapest agreement. Crimea is part of Ukraine and everything that happens in Crimea is happening in Ukraine.

"The independence of Ukraine has been guaranteed by Russia, the US and Britain. Those guarantees said we would live in safety. Those countries must prevent the violence."

Mr Hague said that negotiations were in Russia's interest and persisting on its present course would cost Moscow greatly. "Over time this will be a serious miscalculation for Russia," he said.

A Russian official met Ukraine's ambassador to Moscow last week but otherwise the Kremlin has spurned the caretaker government, claiming it had taken power in an unconstitutional coup.